Incorporating Highly Anisotropic Four-Coordinate Co(II) Ions within One-Dimensional Coordination Chains

Low-coordinate metallic ions have been well recognized for constructing good-performance single ion magnets (SIMs) due to their enhanced magnetic anisotropy; however, the incorporation of such specific ions into coordination polymers is still challenging. Here, we reported two new CoII coordination polymers, namely [Co(pdms)(bpe)]n (1) and {[Co(pdms)(tpb)]center dot H2O center dot tpb}n (2) (H2pdms = 1,2-bis(methanesulfonamido)benzene, bpe = 1,2-di(4-pyridyl)ethane, tpb = 1,2,4,5-tetra(4-pyridyl)benzene). Single crystal X-ray diffraction experiments indicated that the CoII centers in both 1 and 2 display a distorted tetrahedral geometry with quasi C2v symmetry and are linked into a one-dimensional (1D) zig-zag chain via the ditopic bridging ligand of bpe in 1 while a ribbon chain via the tetradentate linker of tpb in 2. Magnetic studies revealed the easy-axis magnetic anisotropy of the CoII ions with different zero -field splitting D of -19 cm-1 (1) and -33 cm-1 (2), likely due to the distinct changes in the Npy-Co-Npy bite angles (100.20 degrees (1) vs. 93.90 degrees (2)). Moreover, slow magnetic relaxation proceeded via different relaxation mechanisms under applied dc fields was observed, giving an effective energy barrier (Ueff) of 69.6 K for 1 and 76.6 K for 2, respectively. The ab initio calculations on both the polymers further confirmed the sign and magnitude of the ZFS parameters and nicely reproduced the experimental results. Our study demonstrated a great potential for applying the well-studied and highly anisotropic 4-coordinate metal ions within a coordination polymer, opening a viable means to tuning magnetic anisotropy via topological control.